In U.S. Pat. No. 4,081,520, assigned to the assignee of this application, the disclosure of which is incorporated herein by reference, there is described a process for the production of chlorine dioxide at high efficiency using sodium chlorate, sulphuric acid and methanol. The mechanism whereby chlorine dioxide is formed is that chlorine which is coproduced with the chlorine dioxide is reacted with the methanol to form chloride ions which then reduce the chlorate ions to form chlorine dioxide and chlorine. The overall reaction may be represented by the following equation: EQU 2NaClO.sub.3 +2H.sub.2 SO.sub.4 +CH.sub.3 OH.fwdarw.2ClO.sub.2 +2NaHSO.sub.4 +HCHO+2H.sub.2 O
The reaction medium from which the chlorine dioxide is formed and which contains sodium chlorate, methanol and sulphuric acid is maintained at its boiling point, generally in the range of about 50.degree. to about 85.degree. C., under a subatmospheric pressure. The evaporated water serves to dilute the chlorine dioxide for removal from the reaction zone. The reaction medium has a high total acid normality in excess of about 9 normal and the by-product deposited from the reaction medium once saturation is reached after start up is a sodium acid sulphate, which may be sodium bisulphate (NaHSO.sub.4) or sodium sesquisulphate (Na.sub.3 H(SO.sub.4).sub.2).
The process of the prior patent is highly efficient in terms of the conversion of chlorate ions to chlorine dioxide. Close to 100% efficiency is attained and the chlorine dioxide is removed from the reaction zone virtually uncontaminated by chlorine, which may be beneficial in many instances of end use of the chlorine dioxide.
The drawback to this prior art process which heretofore has inhibited commercial implementation thereof is the form and nature of the solid by-product. Since the sodium sulphate precipitates in an acid form, removal of this material from the reaction zone results in a loss of the acid values therein. In addition, sodium acid sulphates are difficult to handle physically and exhibit deliquescence.